Journal bearings

ABSTRACT

A plurality of bearing sectors are mounted in a housing. Each sector functions as a lobed area in the bearing to obtain the required lubricant film geometry.

United States Patent 91 Schuller et al.

3,830,552 Aug. 20, 1974 JOURNAL BEARINGS [56] References Cited UNITEDSTATES PATENTS [75] Inventors: Fredrick T. Schuller; Warren A. Moore,both of Cleveland, Ohio [73] Assignee: The Unite states f America as2,322,004 6/1943 308/73 represented by the Administrator of 2,424,0287/l947 Hoeberlem 308/73 the National Aeronautics and SpaceAdministration, Washington, DC Prmary Exammer-Charles Myhre AssistantExaminerFrank Susko Flledi 1973 Attorney, Agent, or Firm-N. T. Musial;G. E. Shook; 21 Appl. No.: 346,483 Mannmg ABSTRACT Related US.Application Data [62] Division of Ser. No. 238,264, March 27, 1972.

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JOURNAL BENGS RELATED APPLICATION This application is a division ofapplication Ser. No. 238,264 which was filed Mar. 27, 1972.

ORIGIN OF THE INVENTION The invention described herein was made byemployees of the United States Government and may be manufactured andused by or for the Government for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention is concerned with theinstability of zero or lightly loaded shafts when they rotate at highspeeds in bearings in low viscosity lubricants. This instability refersto a self-excited fractional-frequency whirl or tendency of the shaftcenter to orbit the bearing center at an angular velocity about halfthat of the shaft around its own center.

This tendency of lightly loaded rotors running at high speeds to orbitor whirl about the bearing center is caused by a film force component,acting at right angles to the line of centers of the journal andbearing, which predominates under light or zero load conditions. Thisself-excited instability produces an outward spiraling of the rotor inthe direction of shaft rotation when the speed is increased. Destructiveseizure may result if the rotor contacts the bearing.

The successful operation of a power generation system for space vehiclesemploying liquid metals as the working fluid depends upon the ability ofa journal bearing to inhibit this instability. Tilting pad bearings havebeen proposed for such applications because these bearings areexceptionally stable. However, tilting pad bearings are complex in thatthey contain several parts and may be subject to pivot surface damage.

SUMMARY OF THE INVENTION These problems have been overcome by utilizingbearings constructed in accordance with the present invention. Eachbearing is of fixed geometry and utilizes a plurality of sectors toprovide lobed areas which function as a pump when the rotor turns. Theresulting pressure distribution is similar to that obtained in ahydrostatic gas bearing.

The geometry of the lubricant film depends on the configuration of thesectors. The film geometry may be converging, diverging, or acombination thereof.

It is, therefore, an object of the present invention to provide animproved journal bearing which may be constructed without expensive andcomplicated machining procedures.

A further object of the invention is to provide an improved journalbearing having removable lobed sectors which are easily replaced in caseof damage.

Another object of the invention is to provide an inexpensive bearinghaving improved stability and simplified damping.

These and other objects of the invention will be apparent from thespecification which follows and from the drawings wherein like numeralsare used throughout to identify like parts.

DESCRIPTION OF THE DRAWINGS Referring now to the drawings:

FIG. 1 is a plan view with parts in section of a bearing constructed inaccordance with the present invention;

FIG. 2 is a section view taken along the line FIG. 22 in FIG. 1;

FIG. 3 is an alternate embodiment of the bearing shown in FIG. 1;

FIG. 4 is an alternate embodiment of the bearing shown in FIG. 3;

FIG. 5 is a perspective view of a sector of the bearing shown in FIG. 4;

FIG. 6 is an alternate embodiment of the sector shown in FIG. 5;

FIG. 7 is another alternate embodiment of the sector shown in FIG. 5;and

FIG. 8 is a cross section view of still another embodiment of a bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,there is shown in FIG. I a bearing 10 constructed in accordance with thepresent invention which produces a converging-diverging film geometry. Alightly loaded shaft 12 rotates at high speed in the bearing 10 in aclockwise direction as indicated by the arrow. This shaft may operatestably at speeds as high as 9,000 rpm under a very light or zero load inlow viscosity fluids such as water.

The bearing 10 comprises a housing in the form of a circular plate 14having a bore 16 extending along the bearing axis for receiving theshaft 12. Suitable holes 18 are provided in the plate 14 for rigidlymounting the bearing and maintaining it in a stationary position as theshaft 12 rotates.

A plurality of rigid posts 20 extend outward from the plate 14 along theshaft 12 as shown in FIGS. 1 and 2. These posts are equally spaced aboutthe bore 16.

According to the present invention a plurality of sectors 22 are mountedon the posts 20 as shown in FIGS. 1 and 2. Each sector 22 comprises apad 24 flexibly mounted to a base 26 with a neck 28 having reducedthickness. In this manner the neck 28 forms a pivot for the pad 24between its leading edge 30 and trailing edge 32.

The minimum radial clearance between the pad 24 and the shaft 12 is atthe neck 28. Both the neck and the minimum radial clearance are locatedat a point approximately sixty percent of the sector arc length measuredfrom the leading edge 30 of each sector.

All of the sectors 22 for each bearing 10 are preferably fabricated froma common cylinder of bearing material. The inside of this cylinder isrough bored to an inside diameter which approximates the outsidediameter of the shaft 12. A plurality of holes 34 are drilled and tappedat the location of each mounting base 26.

The outside surface of the cylinder is machined to the contour of theattached sectors 22. The neck 28 of each sector 22 is machined to thedesired thickness. This thickness is dependent upon the amount offlexibility desired. The cylinder is then cut into the desired number ofpieces to make the sectors 22 for the bearing 10.

The base portion 26 of one sector 22 is inserted into a slot 36 in apost 20. Mounting screws 38 extend through the post 20 and are tightenedinto the threaded holes 34. Taper pin holes 39 are machined, afterassembly, through the post 20 and base portion 26. Taper pins 40 arethen inserted through the post 20 and the base 26 to rigidly secure thesector 22 in the bearing 10.

The surface of the pad 24 is then ground to a radius greater than thatof the shaft 12 with its center offset a predetermined amount in adirection away from the neck 28 of the sector 22. Minimum radialclearance at the neck 28 is achieved by maintaining the axis of thegrinding wheel on a line passing through the center of the bearing andthe base 26. After each sector 22 has been individually finish groundall the sectors are rigidly mounted in the bearing housing.

DESCRIPTION OF ALTERNATE EMBODIMENTS Referring now to FIG. 3 there isshown an alternate embodiment of the invention which is used to producea wholly converging film geometry. This embodiment utilizes a bearingsector 42 comprising a pad 44 rigidly mounted on a base 46. The sectors42 are produced in a manner similar to that used to machine the sectors22 shown in FIGS. 1 and 2.

The sectors 42 are mounted in the posts in the same manner as thesectors 22. The base 46 is formed on the extreme end of the sector 42.No neck of reduced thickness is used in this embodiment. The amount ofsector flexibility is dependent on the wall thickness of the sector 42.The rigid portion of the sector 42 is located at the trailing edge 50 ofthe sector. The minimum radial clearance is at the approximate trailingedge 50 which is the most rigid portion of the sector 42. The maximumradial clearance is at the leading edge 48 which is the most flexibleportion of the sector 42.

The bearing shown in FIG. 4 is similar to the one shown in FIG. 3 withthe exception that the shaft 12 rotates in the opposite direction. Inthis manner the most rigid part of the sector is at the leading edge andthe most flexible portion is at the trailing edge.

In this embodiment a plurality of sectors 52 are mounted in a bore 54 ofa cylindrical bearing housing 56. One of the sectors 52 is shown ingreater detail in FIG. 5.

Each sector 52 has a rigid base 58 as shown in FIGS. 4 to 7 inclusive.The base 58 is mounted in a suitable slot 60 in the housing 56 as shownin FIG. 4. Each sector 52 is held in place in its slot 60 by a pair ofscrews 62 which extend through holes 64 in the housing 56. The screws 62are received in tapped holes 66 in each base 58. When the screws 62 aretightened the base 58 of each sector 52 is rigidly mounted in the slot60.

In this embodiment a pad 68 extends from the base 58in the direction ofrotation of the shaft 12. Each sector 52 has a thin wall and forms acantilevered spring which converges in the direction of shaft rotationtowards the shaft 12. The minimum radial clearance is at the trailingedge of each pad 68. The pads 68 form a wholly converging film geometry.

Referring to the embodiment shown in FIG. 6 the spring action of thecantilevered pad 68 is clamped. This is achieved by bonding a layer 70of suitable damping material to the back surface of each sector 52.

A layer of rubber has been satisfactory for this purpose.

A temperature compensating bearing is shown in FIG. 7. In thisembodiment the sector 52 is a bimetal. One metal layer 71 is bonded tothe sector 52. As the ambient temperature changes, the bi-metallicsector moves away from or towards the shaft 12 depending on thecoefficient of expansion of the two bonded metals.

The inside radius of each bearing sector 52 is rough machined beforeassembly. The sectors 52 are then assembled individually in the bearinghousing 56. The sectors are finish ground individually on the insidediameter by off-setting the center of the bearing housing 56 with thatof the grinding wheel a predetermined amount that will result in aparticular internal bearing geometry desired. After all the sectors 52have been individually ground these sectors are assembled into the axialslots 60.

In the embodiment shown in FIG. 8 no internal offset machining isrequired. In this embodiment a cylinder of a bearing material isassembled into a bearing housing 82 without shimming by subcooling thecylinder, or heating the housing. The cylinder 80 is machined in placeto a predetermined inside diameter. An identification mark 84 isimprinted on one surface of the cylinder 80 and the housing 82.

The cylinder 80 is removed from the housing 82 by subcooling or heatingthe assembly. Suitable shims 86 are placed around the inside diameter ofthe housing 82 in an equally spaced manner. These shims are secured tothe top of the housing 82 by tack welding or taping to preventdislocation during assembly. The thickness of each shim 86 is dependentin part upon the lobe height desired.

The cylinder 80 is again assembled in the shimmed housing 82 bysubcooling the cylinder or heating the housing 82. During the assemblythe identification mark 84 is aligned. When the cylinder 80 and thehousing 82 have reached equilibrium conditions of temperature, an insidediameter trace can be made of the resultant contour. This will identifyaccurately the size of the lobing which has been obtained. The amount oflobing will depend on the thickness of the shims 86 as well as thephysical properties of the bearing housing 82, the shims 86, and thebearing material 80. While various embodiments of the invention havebeen shown and described it will be appreciated that other structuralmodifications may be made without departing from the spirit of theinvention or the scope of the subjoined claims.

What is claimed is:

1. In combination with a lightly loaded shaft rotating at high speedhaving a film of lubricants thereon, an improved bearing comprising astationary housing having a bore extending therethrough from oppositelydisposed ends thereof for receiving said shaft, said bore having asubstantially cylindrical surface,

a cylinder of substantially rigid bearing material inserted in saidbore, said cylinder having an inside diameter concentric with said boreand an outside diameter substantially equal to the diameter of said boreprior to the insertion of said cylinder into said bore, and

a plurality of spaced shims in said bore between said cylinder and saidhousing, said shims being rigidly ment with said bore while otherportions of said outer surface of said cylinder engage said bore therebyforming lobes for shaping the geometry of

1. In combination with a lightly loaded shaft rotating at high speed having a film of lubricants thereon, an improved bearing comprising a stationary housing having a bore extending therethrough from oppositely disposed ends thereof for receiving said shaft, said bore having a substantially cylindrical surface, a cylinder of substantially rigid bearing material inserted in said bore, said cylinder having an inside diameter concentric with said bore and an outside diameter substantially equal to the diameter of said bore prior to the insertion of said cylinder into said bore, and a plurality of spaced shims in said bore between said cylinder and said housing, said shims being rigidly secured to said oppositely disposed ends of said housing to prevent movement thereof as said cylinder is inserted in said bore by subcooling the cylinder or heating the housing, said shims serving to deform said cylinder by maintaining selected portions of the outer surface of said cylinder out of engagement with said bore while other portions of said outer surface of said cylinder engage said bore thereby forming lobes for shaping the geometry of said film. 